1. Field of the Invention
The present invention pertains to the art of filtration and specifically applies to the filtration of a system which is undergoing laminar flow within a conduit. The system is a multiphase system having particulates therein. The particulates have a higher resistance to deformation than the liquid which they are in. The invention is suited to all systems which are undergoing laminar flow both before and during the filtration step. The invention is especially useful in the filtration of high viscosity fluids as high viscosity fluids undergo laminar flow at higher shear stress than low viscosity fluids. Although the present invention is useful for the filtration of "hard" particulates, the present invention is especially suited to the filtration of "soft" partly deformed particulates from a liquid. The invention is conceived to be useful in many areas including textiles, plastics, paints and many other areas in which particulates are removed from a system undergoing laminar flow in a conduit, especially polymers in a liquid state.
2. Prior Art Statement
Prior art in the field of filtration includes the use of structurally similar devices in the filtration of systems undergoing turbulent flow in a conduit (see U.S. Pat. Nos. 3,747,771; 4,119,775; 3,992,886; and 3,718,259). U.S. Pat. No. 3,718,259 pertains to the separation of viscous fluids, and operates upon a completely different principle than the principle of operation of the present invention.
One of the major purposes of the presnt invention is the removal of soft particulates which are very easily deformed (gels, for example). The prior art has been relatively ineffective in removing very soft, easily deformed particulates from relatively viscous fluids. Presently, thick filter cloths installed in high pressure filter presses (in the textile industry for example in processes similar to the process described in U.S. Pat. No. 2,763,636) are used to remove soft, deformable particulates from viscous polymer solutions. The filter presses attempt to separate soft, deformable particulates from the fluid just as hard, relatively nondeformable particulates are removed by the standard filtration techniques commonly used in turbulent flow systems. These thick filter cloths have a limited lifetime because the soft particulates eventually penetrate the felts because the soft particulates are easily deformed under the conditions of filtration so that they eventually squeeze through the thick filter cloths (for a description of the operation of these filter presses in this particular application, see Example I).
In addition to the utilization of filter presses in the removal of soft particulates from viscous solutions, Ronigen-Petter filters have also been used. A Ronigen-Petter filter consists of an outer hollow cylinder (of 10" diameter, for example) and an inner hollow cylinder, the inner cylinder having perforated walls (of 5" diameter, for example). A sock-shaped filter cloth is placed over the perforated portion of the inner cylinder and a viscous liquid having particulates therein (gels in a 2000 poise polymer solution, for example) is pumped into a confined region between the outer and inner cylinders, so that the liquid is then forced against the sock shaped filter cloth with the particulates remaining on the filter cloth. The viscous liquid then permeates the filter cloth, leaving the soft particulates on the surface of the filter cloth. The purified liquid then exits one end of the inner cylinder. A Ronigen-Petter filter has been utilized in place of and in addition to filter presses described above in the filtration of viscous polymer solution produced in accordance with U.S. Pat. No. 2,763,636.
Both the filter press and the Ronigen-Petter filters utilize a method of filtration identical in principle to that used in the filtration of turbulent flow systems (i.e. liquid undergoing turbulent flow both prior to and during the filtration process) and they both accumulate soft particulates upon the filtering medium. Not only do the soft and small particulates eventually penetrate the filter, particulates can also clog the filter if their concentration is high enough. In the use of both types of filters for the purpose of filtering polymer solutions (e.g. polymer solutions as described in U.S. Pat. No. 2,763,636) prior art filters have operated effectively for periods as short as 5 minutes to periods as long as one month, depending upon the particulate concentration.